This invention relates to a cross-connect apparatus having a plurality of cross-connects. More particularly, the invention relates to a cross-connect apparatus which, while reducing the burden of control performed by a controller, is capable of detecting cross-connect abnormality, detecting the cross-connect in which the abnormality has occurred, switching over to a standby cross-connect and switching back to a working cross-connect at the time of recovery.
It is believed that the interfacing of optical signals to optical transmission devices will undergo a shift in emphasis from the handling of serial signals to the handling of parallel signals in the future. The present invention furnishes a cross-connect apparatus, the input to which is an optical parallel signal, with a highly reliable redundant structure and the ability to detect errors within the apparatus at minimum cost.
Structure of Cross-Connect Apparatus According to Prior Art
FIG. 13 is a diagram illustrating the structure of an optical cross-connect apparatus according to the prior art. If m(=4) represents the number of input paths and n(=4) represents the number of bits of each channel arriving in time-shared fashion from each input path, then n-number of m×m working optical cross-connects 1011 to 101n are provided and one standby optical cross-connect 102 is provided for the n-number of working cross-connects. As Illustrated in FIG. 14, an m×m cross-connect has m-number of input terminals and m-number of output terminals (where m=4 holds in the Figure), m-number of input lines and m-number of output lines are arrayed to intersect in the form of a matrix, and a switch is provided at each intersection. In order to implement a cross connection in such a manner that a signal that has arrived at an ith input terminal will be output from a jth output terminal, the switch at the intersection (i,j) is turned on (see the black circles). The Figure illustrates a case where a first input signal is cross-connected to a fourth output, a second input signal to a first output, a third input signal to a third output and a fourth input signal to a second output. It should be noted that although signals on a plurality of channels arrive in time-shared fashion from a single input path, each channel that arrives from an input path #i shall be referred to as an ith channel for the sake of explanation.
Optical signals of first to fourth channels that arrive from optical input paths #1 to #4 are input to optoelectronic transducers (O/E) 1031 to 1034, respectively, upon being converted to n(=4)-bit parallel signals by serial/parallel converters, which are not shown. The optoelectronic transducers 1031 to 1034 convert the optical signals that enter from each of the input paths to electrical signals. A distributor 105i (i=1 to 4) inputs the first to fourth bit signals of a channel i that arrives from input path #i to ith input terminals of respective ones of the first to fourth cross-connects 1011 to 1014 and to a selector 106.
By way of example, the distributor 1051 inputs the first to fourth bit signals of the first channel that arrives from input path #1 to the first input terminals of respective ones of the first to fourth cross-connects 1011 to 1014 and to the selector 106. Similarly, the distributor 1052 inputs the first to fourth bit signals of the second channel that arrives from input path #2 to the second input terminals of respective ones of the first to fourth cross-connects 1011 to 1014 and to the selector 106. If an abnormality occurs in the ith optical cross-connect 101i, the selector 106 selects the ith bit signals of the first to fourth channels that enter the ith optical cross-connect 101i and inputs these to the standby optical cross-connect 102.
Electro-optic transducers (E/O) 1071 to 1074, 108 are provided on the input side of the working and standby optical cross-connects 1011 to 1014, 102, respectively, and optoelectronic transducers (O/E) 1091 to 1094, 110 are provided on the output side of these cross-connects. Signals sent from the first output terminals of the first to fourth cross-connects 1011 to 1014 are converted to electrical signals by the optoelectronic transducers 1091 to 1094, and the electrical signals are input to an electro-optic transducer 1041 via a selector 1111. Similarly, signals sent from the second output terminals of the first to fourth cross-connects 1011 to 1014 are converted to electrical signals by the optoelectronic transducers 1091 to 1094, and the electrical signals are input to an electro-optic transducer 1042 via a selector 1112. Signals sent from the third output terminals of the first to fourth cross-connects 1011 to 1014 are converted to electrical signals by the optoelectronic transducers 1091 to 1094, and the electrical signals are input to an electro-optic transducer 1043 via a selector 1113. Signals sent from the fourth output terminals of the first to fourth cross-connects 1011 to 1014 are converted to electrical signals by the optoelectronic transducers 1091 to 1094, and the electrical signals are input to an electro-optic transducer 1044 via a selector 1114. The electro-optic transducers 1041 to 1044 convert the cross-connected electrical parallel signals input thereto to optical parallel signals and input these parallel signals to parallel/serial converters (not shown). The parallel/serial converters convert the optical parallel signals to optical serial signals and send these signals to prescribed optical output paths #1 to #4.
The first to fourth optical signals of the standby optical cross-connect 102 are converted to electro-optic signals by the optical electro-optic transducer 110, and these signals are input to a distributor 112. If an abnormality occurs in an ith optical cross-connect 101i, the distributor 112 inputs the first output signal of the standby optical cross-connect 102 to an ith terminal on the standby side of the selector 1111, inputs the second output signal of the standby optical cross-connect 102 to the ith terminal on the standby side of the selector 1112, inputs the third output signal of the standby optical cross-connect 102 to the ith terminal on the standby side of the selector 1113, and inputs the fourth output signal of the standby optical cross-connect 102 to the ith terminal on the standby side of the selector 1114. When operation is normal, the selectors 1111 to 1114 select parallel signals of four bits input to the four input terminals of the working channels and input these signals to the electro-optic transducers 1041 to 1044, which constitute the next stage. If an abnormality occurs in the ith cross-connect 101i, however, the selectors 1111 to 1114 select a four-bit signal that is the result of replacing the signals input to the ith input terminals on the working side by signals input to the ith input terminals on the standby side.
A signal cut-off detecting circuit 113 detects cut-off of the signal output from each output terminal of the working optical cross-connects 1011 to 1014, thereby detecting an abnormality in a working cross-connect, and proceeds to notify a controller 115 of the result of detection. A signal cut-off detecting circuit 114 detects cut-off of signals output from the distributor 112, thereby detecting an abnormality in the standby optical cross-connect 102, and proceeds to notify the controller 115 of the result of detection.
Operation
Assume that signals on the first channel that enters from the input path #1 are output upon being cross-connected to the output path #2. As indicated by the dashed lines in FIG. 15, the working optical cross-connects 1011 to 1014 each cross-connect the first input to the second output. Further, the standby optical cross-connect 102 also cross-connects the first input to the second output. Operation is similar with regard to the other input paths as well. Generally, if a signal on an ith channel that arrives from input path #i is output upon being cross-connected to an output path #j, the working optical cross-connects 1011 to 1014 and the standby optical cross-connect 102 each cross-connect the ith input to the jth output.
If the signal cut-off detecting circuit 113 detects cut-off of the signal from, e.g., the working optical cross-connect 1011 in a state in which a signal on the first channel that is input from the input path #1 is cross-connected to the output path #2, then the signal cut-off detecting circuit 113 notifies the controller 115 of result of detection. The controller 115 controls the selector 106, which, as indicated by the dashed lines, selects the first bit signals of the first to fourth channels that are input to the working optical cross-connect 1011 and inputs these signals to the four input terminals of the standby optical cross-connect 102. As a result, the standby optical cross-connect 102 attains an input state identical with that of the working optical cross-connect 1011.
Further, the controller 115 controls the distributor 112 so that the four output signals of the standby optical cross-connect 102 are input to the first input terminals on the standby side of respective ones of the selectors 1111 to 1114 that are the same as those that receive the four output signals of the working optical cross-connect 1011. Furthermore, the controller 115 instructs the selectors 1111 to 1114 to select the signal from the standby optical cross-connect 102 instead of the signal from the working optical cross-connect 1011 as the first bit. As a result, the selectors 1111 to 1114 select the signal from the standby optical cross-connect 102 as the first bit and select the signals from the working optical cross-connects 1012 to 1014 as the second to fourth bits.
By virtue of the foregoing, rescue is possible and cross-connect control can continue even if the working optical cross-connect 1011 develops an abnormality. Similarly, rescue is possible if an abnormality should occur in the other working optical cross-connects 1012 to 1014. If the working optical cross-connect that malfunctioned returns to normal after the changeover is made to the standby optical cross-connect 102, then the original normal state is restored and cross-connect control continues.
Problems
With the conventional optical cross-connect system, it is necessary to control the two selectors, namely the selector 106 on the input side and the selectors 1111 to 1114 on the output side, simultaneously even though changeover of the signal to the standby optical cross-connect 102 is performed when a malfunction occurs. As a consequence, there is an increase in the number of optical parallel signals and an increase in the number of optical cross-connects, resulting in an apparatus of large size. A problem which arises is that there is an increase in load with regard to selector control.
Further, what can be detected by the signal cut-off detecting circuit 113 is only the fact that a signal has been cut off. A problem which results is that signals cannot be checked for error.